The function of these safety supports, which are normally mounted on the rim inside the tire, is to take over the load in the event of tire failure.
The actuation of the support of the tire on the safety bearing might not be perceptible to the driver based on vehicle handling. However, the performance parameters of the tire in this condition are deteriorated, notably because the functional life of these safety bearings is limited. Thus, for safety, the driver be alerted as soon as the support of a tire is actuated on its safety bearing, in order to be able to follow the manufacturer's instructions.
U.S. Pat. No. 4,262,724 discloses a safety bearing comprising circumferential sections having variable radii so as to generate, when travelling using the support, a vibratory excitation in the wheel shaft which warns the driver. U.S. Pat. No. 4,157,726 discloses a safety bearing incorporating two flat surfaces positioned on the outer circumference in order to produce, in addition to the aforementioned vibratory excitation, a rolling noise that can also warn the driver.
These two solutions, which purposely cause deterioration of vehicle behavior when the tire is supported on its safety support, prove suitable when the function of said support is to prevent the instantaneous immobilization of the vehicle in the event of tire failure. On the other hand, when the design of the safety bearing permits the use thereof at a restricted speed over long distances, these solutions are no longer adequate. A safety bearing of this kind is disclosed by Patent No. EP 363 639 the parent patent of which is U.S. 5,363894.
Moreover, many devices have been proposed for detecting the under-inflation of a tire by analyzing the vibrations of the tire/suspension components unit as measured using accelerometers placed on one of the suspension components of the vehicle. These devices monitor changes in the frequency of the first vertical resonance mode of said tire-suspension assembly in the range of approximately 10 to 15 Hz and in conjunction with the reduction of inflation pressure. A device of this kind is disclosed, for example, in U.S. Pat. No. 4,574,267.
However, these devices do not make it possible to detect the actuation of the safety bearing of a tire, since this actuation of support may result not only from a loss of tire inflation pressure, but also from other causes, including tire overload. Accordingly, there is no direct relationship between the inflation pressure of a tire a nd th e actuation of the safety support.
In the following description, the term "wheel-carrier" refers to the parts which actually carry the wheels in the absence of any lack of connection, except for the travelling rotation of said wheels, as well as to the suspension components directly connected to the aforementioned parts and for which the courses of travel are similar.
The expression "non-suspended masses" refers to all of the masses not supported by the suspension springs, i.e., those located between the tires a nd said suspension springs.